A general ozone generation apparatus includes a dielectric electrode and a metal electrode disposed in an airtight vessel. A ring-shaped spacer is inserted between the dielectric electrode and the metal electrode to form a discharge gap. A conductive film is provided on an inner circumference face of the dielectric electrode.
In such an ozone generation apparatus, a raw material gas introduced from a gas inlet into the airtight vessel flows through the discharge gap between the dielectric electrode and the metal electrode, and flows out from a gas outlet.
If a high AC voltage is applied between the dielectric electrode and the metal electrode in parallel with the introduction of the raw material gas, dielectric barrier discharge is formed in the discharge gap and ozone is generated. By the way, dielectric barrier discharge is called simply barrier discharge or silent discharge sometimes.
Heat generated by the dielectric barrier discharge is cooled by cooling water supplied into a cooling water flow path formed by the metal electrode and the airtight vessel. As a result, temperature rise of gas in the discharge gap is suppressed and ozone is obtained efficiently.
In a general conventional ozone generation apparatus, a discharge gap length d is set to be in the range of 0.6 to 1.3 mm. And a gas pressure p of air which is raw material gas is set to be in the range of 0.17 to 0.28 MPa (absolute pressure).
The product of the gas pressure p of the raw material gas and the discharge gap length d is generally called pd product. The law of discharge similarity holds true by making the pd product constant. This is because the pd product represents the number of gas molecules in the discharge gap.
Multiplication of electrons travelling in the discharge gap is represented by the product of the ionization coefficient α of the gas and the discharge gap length d. The αd product is represented byαd=(α/p)(pd)Here, α/p represents ionization caused by single collision, and the pd product represents the number of molecules contained in the discharge gap. This is the reason why the famous Paschen's raw giving a discharge start voltage is a function of the pd product.